The effect of method of application and presence of sulphate on phosphate fixation from three phosphate fertilizers applied to a krasnozem soil

Fixation of phosphate from monocalcium, monoammonium and diammonium phosphate in a krasnozem soil was investigated in two glasshouse trials. The extent of fixation was assessed from the dry matter yield and phosphorus uptake of tomato plants. Less phosphate was fixed from monocalcium phosphate than from the ammonium phosphates, which was attributed to the higher diffusion rates of the latter and to the precipitation of dicalcium phosphate at the site of monocalcium phosphate placement. Banding of sub-optimal quantities of phosphorus increased yields, although the results suggest that banding only temporarily reduces fixation of the ammonium phosphates. Sulphate significantly increased the uptake of phosphorus when added with each of the three P fertilizers. The effect was greater when the fertilizer was banded than when mixed with the soil.